1. Field of the Invention
The present invention generally relates to a wafer supporting unit, and especially relates to a wafer supporting unit for supporting and handling a thin-layer like wafer in a manufacturing process of semiconductor devices.
2. Description of the Related Art
In the manufacturing process of semiconductor devices, a wafer is supported (or held) by a wafer supporting unit (or a wafer holder), and conveyed between processes.
For example, at a back grind process, the rear side of the wafer is ground until the wafer becomes like a thin layer having thickness of about 200 micrometers or less, before the wafer is diced into chips. At this juncture, the thin-layer like wafer is often conveyed to the next process with a protective tape attached for back grinding, is placed on a metal stand and the like, and is diced.
Further, since the temperature of the wafer rises during an ion implantation process, thermally conductive material, such as silicone rubber, is attached on the supporting unit, and the wafer is arranged on the thermally conductive material such that the heat of the wafer is dissipated to the supporting unit. Further, since the thermal conductivity of the thermally conductive material, such as the silicone rubber, is insufficient, a metal porous material with its holes filled with silicone rubber is being studied as a heat transfer object for the wafer supporting unit (JP 62-76146, A). In this case, it is claimed that the thermal conductivity of the heat transfer object is improved, and that the heat transmission characteristics are improved by enhancing adhesion of a wafer to the heat transfer object, improving the total heat transfer.
However, in the former case of the conventional technologies, where only the protective tape is attached to the wafer, the thin-layer like wafer, the mechanical strength of which is degraded, tends to become curved, possibly causing trouble in handling. Further, when processing the wafer, if the wafer with the protective tape is curved on the metal stand, the heat transfer from the wafer to the metal stand is degraded, the wafer cannot be sufficiently cooled, and the protective tape is exposed to a high temperature, quickly causing degradation.
In the latter case, where the heat conduction object is attached to the supporting unit, cooling of the wafer is still not satisfactory.
In view of the above-mentioned problems, the present invention aims at offering a wafer supporting unit that does not produce curvature in the wafer at the time of handling, efficiently cools the wafer by efficiently transferring the heat of the wafer on the wafer supporting unit at the time of wafer processing, and does not thermally degrade the thermally conductive material prepared on the rear side of the wafer side.